AA HistoryHistory andand PreviewPreview ofof SupercontinentsSupercontinents ThroughThrough TimeTime OutlineOutline 1. A Brief History of Supercontinents 2. “Vaalbara”, “Ur” and “Protopangea” The First Supercontinent? 3. “Columbia”- Son of “Ur” 4. Rodinia- The Mad Momma of Supercontinents 5. Pannotia- Fastest supercontinent in the south. 6. Pangea- The forerunner of Amasia 7. Amasia- The future supercontinent. 8. Why do we care how continents are positioned according to the spin axis? - True Polar Wander and Inertial Interchange Events - Dynamics of Plate Motion and Reorganization - Impacts on Climate and Life? - Evolution of the Magnetic Field. The Oldest Supercontinents- A Brief Historical Perspective (PPT) A series of papers in the early 1970’s by Dewey, Burke and Colleagues noted the existence of previous zones of continental rifting and collision foreshadowing the possibility of previous supercontinental assemblages. JDA Piper (1970’s) used the extant paleomagnetic database to propose the existence of a long-lived Precambrian supercontinent which he later dubbed Proto and Paleo-Pangea. The main problem with the Paleo (and Proto) Pangea models is that the paleomagnetic data no longer support this long-lived reconstruction and there are numerous geological problems with the model. In 1984, Gerard Bond and others proposed the existence Russia Scanda of a Neoproterozoic n a v ia supercontinent based upon the ubiquitous presence of passive margin sequences around the South North America globe. They suggested that the America supercontinent broke apart at Africa the Precambrian/Cambrian boundary. Arabia ~600 Ma Iran Passive margins form at Antarctica India locations where rifting of continents begins Subsequent supercontinental models have been forwarded throughout the 1990’s up to the present and include Vaalbara (Zegers and colleagues) “Ur” (Rogers), ProtoPangea (Piper), “Columbia” (Rogers and Santosh, Zhao and colleagues), “Rodinia” (McMenamin and McMenamin; Moores, Dalziel, Hoffman) and “Pannotia” (Powell). That earlier supercontinents should exist is not surprising given the mobile nature of the Earth’s upper thermal boundary layer (e.g. lithosphere) A c o m b Vaalbara Supercontinent: Pre 2.7 i n Ga assembly of the Kaapvaal e d Craton (S. Africa) and the Pilbara s t r Craton (W. Australia) u c t u Cheney (1996) and later Zegers et al. r a (1998) noted that the sequence l , stratigraphic and chronostratigraphic data g showed remarkable similarities between e showed remarkable similarities between o these two cratons. c these two cratons. h r Paleomagnetic tests initially supported the o Paleomagnetic tests initially supported the n configuration (Zegers et al., 1998); o configuration (Zegers et al., 1998); l o however later work Wingate (1998) argued g i against Vaalbara at ~2.8 Ga. c a l , a n d p a l a e o “Ur” Rogers (1996) also noted that the Kaapvaal craton, the Pilbara craton, the Western Dharwar craton (India) the Singhbhum craton (India) and portions of coastal east Antarctica were all “stabilized” (e.g. accumulated platform sediments that were left undeformed) by 3.0 Ga. He linked these together in a single landmass which he named “Ur”. Subsequent growth of Ur occurred to form the East Gondwana landmass. The Growth of “Ur” from 3.0 to 1.5 Ga according to Rogers (1996). “Ur” in Younger Supercontinents- Piper’s ProtoPangea Piper (1982, 1987, 2000, 2003) has argued repeatedly that the paleomagnetic data support a long-lived Precambrian Arctica supercontinent. A careful examination of paleomagnetic poles with good age control shows gross inconsistencies with this model. Atlantica This model needs to be considerably revised or completely discarded (Van der Ur Voo and Meert, 1991; Meert and Torsvik, 2004). The “Columbia” Supercontinent (Rogers and Santosh, 2002; Zhao et al., 2004) Rogers and Santosh (2002) concluded that a supercontinent called “Columbia” was assembled during the interval from ~1.9-1.8 Ga. Key observations supporting their hypothesis were cited as: - The existence of numerous 1.9-1.8 Ga orogenic belts - A series of ~1.5 Ga rift basins associated with the breakup of the supercontinent. Zhao et al. (2002, 2003, 2004) Updates to Columbia Zhao et al. have detailed the evidence for Columbia in a series of papers, Specific evidence cited by Zhao et al. for their version of Columbia includes: •The formation of Nuna (Gower et al., 1990) composed of the North American protocraton and possibly Baltica (northern Europe) during the interval from 2.1-18. Ga. • Presence of 2.1-1.8 Ga orogenic belts (these include the Trans-Hudson; Penokean; Taltson-Thelon; Wopmay; New Quebec; Torngat; Foxe; Makkovik-Ketilidian; Ungava; Nugssutoqidian; Kola-Karelian; Svecofennian; Volhyn; Palchema; Akitkan; Transantarctic; Capricorn; Limpopo; Transamazonia; Eburnean; Trans North China; Central Indian Tectonic Zone; Central Aldan; Halls Creek). •Continental Rift Basins and ‘anorogenic’ magmatism beginning ~1.6 Ga. Distribution by continent of 2.1-1.8 Ga orogenic belts as described by Zhao et al. (2004) The ‘Columbia” Supercontinent of Zhao et al., 2004. The Demise of the Columbia Supercontinent at 1.5 Ga (Zhao et al., 2004) The Rodinia Supercontinent First proposed by McMenamin and McMenamin (1990) as the birthplace for the Cambrian explostion. Later Moores (1991) proposed a link between the SW US and East Antarctica and Australia (SWEAT) during the Mesoproterozoic and called this the SWEAT fit. Shortly thereafter (Dalziel, 1991) proposed a supercontinent based partly on the SWEAT hypothesis. This was followed by a proposal from Hoffman (1991) and a decade long series of papers examining the evidence for Rodinia. Data supporting a supercontinent during the Meso-Neoproterozoic: 1.1-0.9 Ga Orogenic Belts Neoproterozoic rift basins and passive margin sequences around the globe. Geologic, geochronologic and paleomagnetic evidence are supportive but often highly divergent on the exact makeup of the SC. WhatWhat diddid RodiniaRodinia LookLook Like?Like? ‘Traditional’ Rodinia(?) -How were continents distributed along the t if R a M 00 -7 western margin of 0 western margin of 80 Mozambique Laurentia? Ocean 60 0-550 M a Rift -Where does Siberia fit? Brasiliano Ocean -What continents occupied the SW and E Laurentian margins? 1: Meert and Torsvik IssuesIssues withwith thethe NorthernNorthern andand WesternWestern MarginsMargins ofof LaurentiaLaurentia • SWEAT, AUSWUS, AUSMEX, SIBCOR or ?? Siberia? AUS Baltica (SWEAT) • When did rifting occur? ANT RKS (SWEAT) Subsidence data says AUS (AUSWUS) Laurentia ~550 Ma, most models RP RKS posit an earlier 700-800 Amazonia posit an earlier 700-800 ANT K2 Ma rifting. (AUSWUS) K3 SFC K1 SFC Congo Congo DB K4 DB From: Meert and Torsvik (in press) Meert and Torsvik, 2003 SiberiaSiberia •• 33 DistinctDistinct fitsfits – Arctic Margin with a variety of orientations (e.g. Pelechaty, 1996; Rainbird et al., 1998; Frost et al., 1998; Condie and Rosen, 1994) – Cordilleran Margin (e.g. Sears and Price, 2000) – Not part of younger Rodinia (e.g. Hartz and Torsvik, 2002; Meert and Torsvik, 2003) KalahariKalahari--CongoCongo There have been any number of fits proposed for the Kalahari & Congo Craton. These myriad fits are primarily based on: Laurentia A. ‘Need’‘Need’ forfor aa southernsouthern continent to collide with Powell et al. (2001) Dalziel et al. (2000) K2 DB DB S-SW US during K3 S-SW US during DB SFC K1 Grenvillian times (Dalziel Congo SFC Weil et al. (1998) et al., 2000). Meert & Torsvik (in press) Congo DB B. Comparison of APWP’s K4 DB from Laurentia-Congo and Kalahari (Weil et al., 1998; Powell et al., 2001; Figure 3a: Meert and Torsvik (in press) Meert and Torsvik, 2003) AmazoniaAmazonia:: New paleomagnetic data from Tohver et al. (2002) hint that Amazonia might be the ‘southern’ continent. AUS Baltica (SWEAT) t if R ANT RKS a M (SWEAT) 0 70 0- 80 RP Laurentia Mozambique Ocean RKS 6 Amazonia 00-550 Ma Rif t K3 SFC K1 Brasiliano SFC Ocean Congo Congo DB K4 DB 1: Meert and Torsvik Figure 3a: Meert and Torsvik BalticaBaltica ~1225 Ma Laurentia Baltica RKS Amazonia Figure 3b: Meert and Torsvik This fit is made by using “SPUEG” Fit (750 Ma; Hartz & paleomagnetic data from Baltica Torsvik, 2002). (Pesonen et al., in press) at 1225 Note: Fit works for 1100-1000 Ma poles, Ma and fitting the 1.55-1.60 but not for 930-850 Ma suggesting some rapikivi suites from Amazonia readjustments between Baltica-Laurentia and Baltica (Geraldes et al., 2001) IssuesIssues W/W/RodiniaRodinia 1. Mesoproterozoic to Early Neoproterozoic Fits between continental blocks are critically dependent on choice of paleomagnetic data (including polarity) and choice of geologic links. 2. New paleomagnetic data challenge ‘traditional’ Rodinia models—especially with respect to the Australia-Antarctic blocks and Amazonia. 3. The new paleomagnetically based models leave significant lengths of Neoproterozoic Laurentian passive margin sequences with no conjugate. 4. Geologic links can be used to argue for nearly any fit (or no fit) between the various cratons thought to compose Rodinia. 5. Nearly 20 years since the Bond et al. proposal and a dozen years since the McMenamin and McMenamin proposal, we still have no definitive configuration for Rodinia. Pannotia (Powell, 1995) The existence of Pannotia is predicated on the notion that Gondwana assembly was completed prior to the opening of the Iapetus Ocean along the eastern margin of Laurentia. Timing is crucial- Gondwana assembly appears to have culminated somewhere between 570-530 Ma (Meert, 2003). Rifting in northeastern Laurentia and Baltica began around 615 Ma (Kamo et al., 1989; Svenningsen, 2001). Paleomagnetic data are somewhat equivocal, but at best this supercontinent would have existed for no more than 15-20 Ma. The breakup of Pannotia may have been quite rapid. This rapid transition has led to numerous hypotheses regarding the dynamics of plate driving mechanisms and/or episodes of true polar wander (Kirschvink et al., 1997; Evans, 1998; Meert, 1999; Meert and Tamrat, 2003; Evans, 2002, Meert and Lieberman, 2004).